A lithium ion nonaqueous electrolyte secondary battery has achieved widespread use in various fields such as electric vehicles, power storage, and information devices as a high energy-density battery. Accordingly, market requirements for the nonaqueous electrolyte secondary battery grow further and research thereon is actively conducted.
Among others, for use as an electric source for vehicles such as electric vehicles, a lithium ion nonaqueous electrolyte secondary battery is required to have a high energy density, that is, a large discharge capacity per unit weight or unit volume.
On the other hand, requirements of safety grow along with an increasing discharge capacity per unit weight or unit volume. One answer thereto is an all-solid-state secondary battery. The all-solid-state secondary battery is a secondary battery literally using a solid electrolyte, instead of the conventional nonaqueous electrolyte, that is, an organic electrolyte solution. The organic electrolyte solution is inflammable and thus, development of technology is actively under development to improve safety when the organic electrolyte solution is used. Nevertheless, it is difficult to ensure sufficient safety. On the other hand, since the all-solid-state secondary battery does not use any organic electrolyte solution, the all-solid-state secondary battery is not apt to ignite, and therefore can form an extremely safe secondary battery.
Further, according to the all-solid-state secondary battery, since no electrolyte solution is used, there can suitably be formed an electrode in a bipolar structure obtained by applying a positive electrode and a negative electrode to the front side and the back side of a current collector, and a bipolar battery obtained by stacking such electrodes after coating a solid electrolyte thereon. In such a bipolar battery, the voltage can be made high within a cell.